Gas-to-water heat exchanger

ABSTRACT

A heat exchanger is disclosed for cooling a gas from a first temperature to a second temperature. The exchanger comprises a first heat exchanging chamber, a second heat exchanging chamber and an array of heat pipes which are arranged to extend from within the first heat exchanging chamber to within the second heat exchanging chamber. The first heat exchanging chamber comprises an inlet for receiving a coolant into the chamber and an outlet through which the coolant can exit the first chamber, the coolant being arranged to pass over the portion of the heat pipes which extend within the first chamber. The second heat exchanging chamber comprises an inlet for receiving the gas at a first temperature into the chamber and an outlet through which the gas can exit the second chamber at a second temperature. The gas is arranged to pass along the second chamber between the inlet and the outlet, along a path comprising a substantially constant cross-sectional area to minimize the pressure drop between the inlet and the outlet.

CROSS REFERENCE TO RELATED APPLICATIONS

This non-provisional application claims the benefit of provisionalapplication No. 61/612,251 filed on Mar. 17, 2012, entitled“Gas-to-Water Heat Exchanger”, including Appendix A, which applicationand appendix are incorporated herein in their entirety by thisreference.

BACKGROUND

The present invention relates to a heat exchanger and particularly, butnot exclusively to a heat exchanger comprising heat pipes.

A heat pipe is a hermetically sealed evacuated tube typically comprisinga mesh or sintered powder wick and a working fluid in both the liquidand vapour phase. When one end of the tube is heated the liquid turns tovapour upon absorbing the latent heat of vaporization. The hot vapoursubsequently passes to the cooler end of the tube where it condenses andgives out the latent heat to the tube. The condensed liquid then flowsback to the hot end of the tube and the vaporization-condensation cyclerepeats. Since the latent heat of vaporization is usually very large,considerable quantities of heat can be transported along the tube and asubstantially uniform temperature distribution can be achieved along theheat pipe.

It is known to utilize a heat exchanger comprising separated chambersand a plurality of heat pipes which extend between the chambers, suchthat heat can become transferred from one chamber to the other. In thisrespect, by passing a heated fluid through one chamber, the heat pipescan transfer the heat absorbed from the heated fluid to the otherchamber wherein a cooled fluid may pass to subsequently absorb the heatfrom the heat pipes.

However, when passing a fluid through a chamber of the heat exchanger itis found that the pressure drop between an inlet and an outlet of therespective chamber can be significant. This is found to reduce the heattransfer efficiency between the fluid and the heat pipes within thechamber with the result that the heat can rapidly increase to dangerouslevels within the chamber.

SUMMARY

We have now devised an improved heat exchanger which alleviates theabove-mentioned problem.

In accordance with the present invention, there is provided a heatexchanger for cooling a gas from a first temperature to a secondtemperature, the exchanger comprising a first heat exchanging chamber, asecond heat exchanging chamber and an array of heat pipes which arearranged to extend from within the first heat exchanging chamber towithin the second heat exchanging chamber;

the first heat exchanging chamber comprising an inlet for receiving acoolant into the chamber and an outlet through which the coolant canexit the first chamber, the coolant being arranged to pass over theportion of the heat pipes which extend within the first chamber;

the second heat exchanging chamber comprising an inlet for receiving thegas at a first temperature into the chamber and an outlet through whichthe gas can exit the second chamber at a second temperature; wherein,

the gas is arranged to pass along the second chamber between the inletand the outlet along a path comprising a substantially constantcross-sectional area to minimize the pressure drop between the inlet andthe outlet.

The provision of a substantially uniform cross-sectional area for thegas flow reduces regions of significant pressure gradients within thechamber. The heat exchanger of the present invention thus ensures aminimal pressure drop and thus a substantially uniform transfer of heatbetween the gas and the heat pipes at all positions within the chamber.

Preferably, the second heat exchanging chamber further comprises adeflection plate which is arranged to deflect the passage of gas acrossthe heat pipes in passing between the inlet and the outlet of the secondchamber. The deflection plate is arranged to cause the gas to passpredominantly across the heat pipes as opposed to along the heat pipesto increase the thermal transfer between the heat pipes and the gas andthus the thermal transfer between the first and second chambers.

The deflection plate preferably extends substantially radially of thesecond chamber and comprises an outer periphery which is spaced from aside wall of the second chamber. The gas is thus arranged to passthrough an annular aperture defined between the outer periphery of thedeflection plate and the side wall of the chamber, in passing betweenthe inlet and the outlet of the second chamber.

The inlet and outlet of the second chamber are preferably disposed on alongitudinal axis of the heat exchanger.

Preferably, the deflection plate comprises a gate disposed therein whichis arranged to open and close a central region of the deflection plate.The gate serves as a valve to control the passage of gas direct from theinlet to the outlet of the second chamber, through the plate. The gatepreferably comprises a butterfly valve.

The outlet of the first chamber preferably comprises a sensor forsensing the temperature of the liquid exiting the first chamber. Thegate is preferably arranged to open and close in dependence on thesensed temperature of the liquid exiting the first chamber.

Preferably, the array of heat pipes comprises heat pipes arranged insubstantially concentric circular rows. The heat pipes are preferablyorientated substantially parallel to each other.

The rows of heat pipes preferably comprise a plurality of flowdisturbers disposed at separated positions along the rows and whichserve to create a turbulent flow of liquid within the row. The flowdisturbers preferably comprise a plurality of rods which extend alongthe length of the first chamber substantially parallel to the heatpipes. Successive rods along each row are preferably disposed atopposite sides of the row to redirect the flow of liquid along the row.

The first and second heat exchanging chambers are preferably separatedby a separation plate, through which the heat pipes extend. Preferably,the heat pipes extend in sealing relation with the separation plate viasealing means. Preferably, the sealing means comprises a collarseparately disposed around each heat pipe which is arranged to compressa sealing ring against the separation plate.

The first chamber preferably further comprises a compression platedisposed above the heat pipes, which is arranged to abut the upperregion of the heat pipes at one side thereof and comprises a pluralityof compression springs disposed on the other side thereof.

The compression springs are preferably arranged to extend against a lidof the first chamber and act to urge the compression plate against theheat pipes and thus the heat pipes within the separation plate. Duringoperation of the heat exchanger the temperature of the heat pipes willincrease and it is found that this temperature increase causes a smallexpansion of the heat pipes. The compression plate and springs enablethe heat pipes to freely expand while maintaining a bias of the heatpipes toward the separation plate.

Note that the various features of the present invention described abovemay be practiced alone or in combination. These and other features ofthe present invention will be described in more detail below in thedetailed description of the invention and in conjunction with thefollowing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the present invention may be more clearly ascertained,some embodiments will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a longitudinal sectional view of a heat exchanger according toan embodiment of the present invention;

FIG. 2 is a transverse sectional view of the heat exchanger of FIG. 1taken across line A-A;

FIG. 3 is a transverse sectional view of the heat exchanger of FIG. 1taken along line B-B;

FIG. 4 is a plan view of the baffle disposed within the second chamber;

FIG. 5 is a magnified longitudinal sectional view of a heat pipedisposed within a separation plate, illustrating the sealing means;

FIG. 6 is a magnified view of a spring disposed upon the compressionplate; and

FIG. 7 is a transverse sectional view of the heat exchanger of FIG. 1taken across line B-B, with side walls of the heat exchanger opened.

DETAILED DESCRIPTION

The present invention will now be described in detail with reference toseveral embodiments thereof as illustrated in the accompanying drawings.In the following description, numerous specific details are set forth inorder to provide a thorough understanding of embodiments of the presentinvention. It will be apparent, however, to one skilled in the art, thatembodiments may be practiced without some or all of these specificdetails. In other instances, well known process steps and/or structureshave not been described in detail in order to not unnecessarily obscurethe present invention. The features and advantages of embodiments may bebetter understood with reference to the drawings and discussions thatfollow.

Referring to FIGS. 1 to 3 of the drawings, there is illustrated a heatexchanger according to an embodiment of the present invention. The heatexchanger 10 comprises a first heat exchanging chamber 11 and a secondheat exchanging chamber 12. Each chamber 11, 12 comprises asubstantially cylindrical housing 13, 14, which are mounted one on topof the other such that a longitudinal axis of the first chamber 11extends in a substantially collinear relationship with a longitudinalaxis of the second chamber 12 and thus the heat exchanger 10.

The first chamber 11 of the heat exchanger 10 is disposed above thesecond chamber 12 and comprises an inlet 15 and an outlet 16 which aredisposed within an arcuate side wall of the housing 13. The inlet andoutlet 15, 16 of the first chamber 11 are arranged to enable a liquidcoolant such as water, to pass into and out from the chamber 11,respectively. The first chamber 11 further comprises a passage 17 whichextends along the first chamber 11 substantially along the longitudinalaxis thereof. The passage 17 is defined by a substantially cylindricalwall 18 which seals the interior of the first chamber 11 from thepassage 17, and extends between an opening 19 disposed in an upper endwall 20 of the first chamber 11 to an upper region of a separation plate21.

Referring to FIG. 4 of the drawings, the separation plate 21 comprises afirst aperture 22 disposed substantially at the centre thereof which isarranged to align with the cylindrical wall 18 defining the passage 17,such that the wall 18 extends substantially around a periphery of thefirst aperture 22. The second chamber 12 is secured to the underside ofthe separation plate 21 and thus the first chamber 11, and comprises aninlet 23 disposed substantially upon the longitudinal axis of thechamber 12, within a lower end wall 24 thereof. The first aperture 22disposed within the separation plate 21 and the passage 17 serve as anoutlet of the second chamber 12, such that the gas to be cooled forexample, is arranged to pass into the second chamber 12 through theinlet 23 disposed in the lower end wall 24 of the second chamber 11 andout of the second chamber through the first aperture 22 and along thepassage 17.

The heat exchanger 10 further comprises a plurality of substantiallylinear heat pipes 25 which extend from within the first chamber 11,through an array of second apertures 26 disposed within the separationplate 21 around the first aperture 22, and terminate in the secondchamber 12 so as to enable heat to be transferred between the chambers11, 12. The heat pipes 25 extend substantially parallel to thelongitudinal axis of the first and second chambers 11, 12 and areconfigured in a substantially concentric arrangement of rows of heatpipes 25, as illustrated in FIGS. 2 and 3 of the drawings, centeredsubstantially on the longitudinal axis. In this manner each chamber 11,12 comprises a plurality of arcuate rows of heat pipes 25, havingdifferent radii of curvature.

Adjacent circular rows of heat pipes 25 within the first chamber 11 areseparated by a wall 26 which extends along the length of the firstchamber 11 and defines a channel 27 along which the liquid can flow.Adjacent walls 26 comprise an aperture 28 disposed at opposite endsthereof such that the liquid is cause to flow in a clockwise direction,for example, within the channel 27 in passing across one row of heatpipes 25 substantially around the chamber 11, before passing radially ofthe chamber 11 to the adjacent row of heat pipes 25, and subsequently ina counter-clockwise direction in passing across the heat pipes 25 in theadjacent row.

The channel 27 disposed in the first chamber 11 further comprises aplurality of rods 29 which extend substantially parallel to each otherand the longitudinal axis of the heat exchanger 10. The rods 29 aredisposed along the channel 27 between the heat pipes 25, and successiverods 29 along the channel 27 are disposed at opposite sides of thechannel 27 to prevent the liquid from simply passing around a side ofthe channel 27 without significantly extracting the heat from the heatpipes 25. The rods 27 act to create a turbulent flow within the channel27 and thus encourage the interaction of the liquid with the heat pipes25 to maximize the transfer of heat between the heat pipes 25 and theliquid.

The second chamber 12 comprises a deflection plate or baffle 30 whichextends across the chamber 12, substantially transverse the longitudinalaxis of the chamber 12, between the inlet 23 and the outlet regiondefined by the first aperture 17 in the separation plate 21. The baffle30 extends substantially radially of the second chamber 12 from acentral region thereof, and comprises an outer periphery which is spacedfrom the housing 14 of the second chamber 12 to define an annularpassage 31. The heat pipes 25 are arranged to extend through apertures30 a in the baffle 30 in sealing relation therewith, such that the gasis arranged to pass across the heat pipes 25, through the annularpassage 31, and back across the heat pipes 25, in moving from the inlet23 to the outlet region of the second chamber 12.

The baffle 30 comprises a gate or valve 32, such as a butterfly valve,which can be configured between a fully open state in which the gas isarranged to pass direct from the inlet 23 to the outlet region withoutsubstantially passing through the annular passage 31, a closed state inwhich the majority of the gas is arranged to pass through the annularpassage 31 in passing from the inlet 23 to the outlet region of thesecond chamber 12, and various intermediate states in which a portion ofthe gas is arranged to pass through the valve 32 and a portion of thegas is arranged to pass through the annular passage 31. Thecross-sectional area of the annular passage 31 is substantially matchedto the cross-sectional area of the inlet 23 and outlet region of thesecond chamber 12 to minimize the pressure drop of the gas between theinlet 23 and outlet region of the second chamber 12.

Referring to FIG. 5 of the drawings, the heat pipes 25 are supportedwithin the heat exchanger 10 by the separation plate 21 via a series ofcollars 33 disposed upon the heat pipes 25. The collars 33 are arrangedto extend within each of the second apertures 26 and serve to seal theheat pipes 25 to the separation plate 21, such that the interior of thefirst and second chambers 11, 12 remain isolated from each other.

The second apertures 26 comprise an internal flange 34 which extendsinto the respective second aperture 26 to reduce the diameter of thesecond aperture 26 at the side of the plate 21 adjacent the secondchamber 12. The flanges 34 separately act as a seat for a sealing ring35, such as an O-ring, such that the collars 33 separately disposed uponthe heat pipes 25 are arranged to extend into the respective aperture 26from within the first chamber 11 and compress the sealing ring 35against the flange 34 and the heat pipe 25, to seal the heat pipe 25within the separation plate 21.

The longitudinal ends of the heat pipes 25 disposed within the secondchamber 12 are uncoupled and separated from the lower end wall 24 of thesecond chamber 12, whereas the longitudinal end of the heat pipes 25disposed within the first chamber are arranged to abut the underside ofa compression plate 36. The compression plate 36 is substantiallyannular in shape, and is sized to extend between the cylindrical wall 18defining the passage 17 and the arcuate side walls 13 of the firstchamber 11.

The upper side of the compression plate 36 comprises a plurality ofcompression springs 37 which are arranged to abut the upper wall 20 ofthe first chamber 11, as illustrated in FIG. 6 of the drawings. When theupper wall 20 is secured upon the first chamber 11 to seal the firstchamber 11, the springs 37 are arranged to partially compress to urgethe compression plate 36 upon the upper ends of the heat pipes 25 andthus bias the heat pipes 25 into the second apertures 26 to maintain theseal between the heat pipes 25 and the separation plate 21. During useit is found the increase in temperature of the heat pipes 25 causes theheat pipes 25 to expand which can cause thermal stresses to developwithin the heat exchanger 10. The compression plate 36 and springs 37enable the heat pipes to expand to relieve any stresses which develop,while maintaining an intimate seal of the heat pipes within the secondapertures of the separation plate 21.

In use, the gas to be cooled is arranged to pass into the second chamber12 via the inlet 23 and subsequently pass radially outwardly across theheat pipes 25 due to the baffle 30, through the annular passage 31. Thegas is then caused to pass radially inwardly of the second chamber 12,back across the heat pipes 25 toward the outlet region. As the gaspasses across the heat pipes 25, the heat associated with the gasbecomes transferred to the heat pipes 25, causing the gas to becomecooled. The heat transferred to the heat pipes 25 is then communicatedalong the heat pipes 25 to the first chamber and becomes extractedtherefrom by the flow of liquid, for example water, within the channel27. The outlet 16 of the first chamber comprises a sensor (not shown),for example a thermocouple sensor, for sensing the temperature of theliquid exiting the chamber 11. If the monitored temperature of theliquid rises above a threshold value, then in order to control theamount of heat recovered from the gas, the valve 32 on the baffle 30 isopened accordingly to vent a portion of the gas direct to the outletregion and thus reduce the amount of heat transferred between the gasand the heat pipes 25.

Referring to FIG. 7 of the drawings, the arcuate walls 14 of the secondchamber 12 may be hinged or otherwise removable from the heat exchangerto provide for access into the chamber 12 for cleaning and maintenance.The skilled reader will recognize however, that the arcuate side walls13 of the first chamber 11 may also be hinged or removable for cleaningand maintenance.

For further details of the present invention, please see attachedAppendix A.

While this invention has been described in terms of several embodiments,there are alterations, modifications, permutations, and substituteequivalents, which fall within the scope of this invention. It shouldalso be noted that there are many alternative ways of implementing themethods and apparatuses of the present invention. It is thereforeintended that the following appended claims be interpreted as includingall such alterations, modifications, permutations, and substituteequivalents as fall within the true spirit and scope of the presentinvention.

What is claimed is:
 1. A heat exchanger for cooling a gas from a firsttemperature to a second temperature, the exchanger comprising a firstheat exchanging chamber, a second heat exchanging chamber and an arrayof heat pipes which are arranged to extend from within the first heatexchanging chamber to within the second heat exchanging chamber; thefirst heat exchanging chamber comprising an inlet for receiving acoolant into the chamber and an outlet through which the coolant canexit the first chamber, the coolant being arranged to pass over theportion of the heat pipes which extend within the first chamber; thesecond heat exchanging chamber comprising an inlet for receiving the gasat a first temperature into the chamber and an outlet through which thegas can exit the second chamber at a second temperature; wherein, thegas is arranged to pass along the second chamber between the inlet andthe outlet along a path comprising a substantially constantcross-sectional area to minimize the pressure drop between the inlet andthe outlet.
 2. A heat exchanger according to claim 1, further comprisinga deflection plate which is arranged to deflect the passage of gasacross the heat pipes in passing between the inlet and the outlet of thesecond chamber.
 3. A heat exchanger according to claim 2, wherein thedeflection plate is arranged to cause the gas to pass predominantlyacross the heat pipes as opposed to along the heat pipes.
 4. A heatexchanger according to claim 2, wherein the deflection plate extendssubstantially radially of the second chamber and comprises an outerperiphery which is spaced from a side wall of the second chamber.
 5. Aheat exchanger according to claim 2, wherein the deflection platecomprises a gate disposed therein which is arranged to open and close acentral region of the deflection plate.
 6. A heat exchanger according toclaim 5, wherein the outlet of the first chamber comprises a sensor forsensing the temperature of the liquid exiting the first chamber.
 7. Aheat exchanger according to claim 6, wherein the gate is arranged toopen and close in dependence on the sensed temperature of the liquidexiting the first chamber.
 8. A heat exchanger according to claim 1,wherein the inlet and outlet of the second chamber are disposed on alongitudinal axis of the heat exchanger.
 9. A heat exchanger accordingto claim 1, wherein the array of heat pipes comprises heat pipesarranged in substantially concentric circular rows.
 10. A heat exchangeraccording to claim 1, wherein the heat pipes are orientatedsubstantially parallel to each other.
 11. A heat exchanger according toclaim 1, wherein the rows of heat pipes comprise a plurality of flowdisturbers disposed at separated positions along the rows and whichserve to create a turbulent flow of liquid within the row.
 12. A heatexchanger according to claim 11, wherein the flow disturbers comprise aplurality of rods which extend along the length of the first chambersubstantially parallel to the heat pipes.
 13. A heat exchanger accordingto claim 12, wherein successive rods along each row are disposed atopposite sides of the row to redirect the flow of liquid along the row.14. A heat exchanger according claim 1, wherein the first and secondheat exchanging chambers are separated by a separation plate, throughwhich the heat pipes extend.
 15. A heat exchanger according to claim 14,wherein the heat pipes extend in sealing relation with the separationplate via sealing means.
 16. A heat exchanger according to claim 15,wherein the sealing means comprises a collar separately disposed aroundeach heat pipe which is arranged to compress a sealing ring against theseparation plate.
 17. A heat exchanger according to claim 1, wherein thefirst chamber further comprises a compression plate disposed above theheat pipes, which is arranged to abut the upper region of the heat pipesat one side thereof and comprises a plurality of compression springsdisposed on the other side thereof.
 18. A heat exchanger according toclaim 17, wherein the compression springs are arranged to extend againsta lid of the first chamber and act to urge the compression plate againstthe heat pipes and thus the heat pipes within the separation plate.